This invention relates to the use of known chromium +3 carboxylates as catalysts for reaction of small ring systems, such as aziridines, oxetanes, lactones, carbonate esters, and thiiranes, and for reaction of hydroxy compounds with anhydrides in monomeric or polymeric reactions.
The literature is replete with information showing how to react epoxides with carboxylic acids, anhydrides and imides at room or elevated temperatures. As shown in Catalysis in Polymer Synthesis, ACS Symposium Series 496, Edited by E. J. Vandenberg (1992), aluminum porphyrins, mixed with quaternary salts of the type R4PX and R4NX, are used to catalyze the reaction of an epoxy with carbon dioxide or anhydrides, but high temperature and/or long reaction times are generally needed. Elastomer modified epoxy resins such as diglycidyl ether of bisphenol A (DGEBA) can be made to react with carboxy-terminated polybutadiene-acrylonitrile (CTBN) using triphenyl phosphine, but high reaction temperature or long reaction time is needed to achieve complete reaction. There are a large number of amines, such as polyamide resins like Versamid(copyright), diethylenetriamine, methylenedianiline, that are used to cure various epoxy systems but frequently the cure time is very long and accelerators, such as resorcinol, are required. Catalysts, such as the aluminum alkyls (which tend to be very pyrophoric) have been used to promote homo or block polymerization of epoxides, thioepoxides, selenoepoxides and oxetanes. Aziridines have been homopolymerized using a variety of acid catalysts. U.S. Pat. No. 3,635,869 (1972) discloses use of chromium+3 carboxylate salts to accelerate the reaction of epoxides with carboxylic acids, anhydrides and imides at room temperature or elevated temperatures.
General references to various catalytic systems include Epoxy Resin Chemistry II, ACS Symposium Series 221, Edited by R. S. Bauer (1983). However, such references do not show the use of chromium+3 carboxylates to catalyze ring systems with carboxy-containing compounds, such as carboxylic acids, anhydrides, imides, lactones and carbonate esters.
It is among the objects and advantages of the invention to employ chromium, Cr+3, catalysts, particularly in the form of carboxylate salts, to catalyze ring systems selectively to block copolymers and end-reactive polymers with controlled molecular weight through the control of catalyst concentration, reaction temperature, and reaction time. It is another object and advantage of the invention to increase by up to several orders of magnitude the reaction rates of the single reaction or the polymerization of ring systems with carboxylic acids, anhydrides, imides, lactones and carbonate esters, and to produce novel prepolymers, polymers, compositions, and compounds, including compounds of pharmaceutical use.
The invention comprises the use of Cr+3 salts, e.g., chromium+3 carboxylate salts such as octoates, acetates, butyrates, benzoates, and the like, to enhance or accelerate the reaction of aziridines, oxetanes, thiiranes and oxiranes with carboxylic acids, anhydrides, imides, lactones and carbonate esters to form monomeric or polymeric reaction products. Equally important, chromium+3 carboxylate salts of the invention are used to enhance or accelerate the reaction of hydroxy compounds with anhydrides, lactones, and carbonate esters.
This invention is significant because it discloses the use of chromium+3 carboxylates to promote reactions of small ring systems and hydroxy compounds and finds unique application in the preparation and manufacture of non-polymeric chemicals, new plastic and polymeric materials as well as in improving the reaction or processing conditions of already existing non-polymeric, polymeric and plastic materials. A suitable Cr+3 catalyst is HYCAT(trademark) 2000, containing chromium+3 octoate, available from Dimension Technology Chemical Systems, Inc. of Fair Oaks, Calif.
One advantage of the Cr+3 carboxylate catalysts of the invention over existing catalysts is that they do not promote homopolymerization of any of the reactants. The use of Cr+3 catalysts results in the synthesis of block copolymers and end-reactive polymers with controlled molecular weight. By adjusting the concentration of the catalyst and reaction temperature, the reaction time can be accurately controlled. Another advantage is that the Cr+3 catalysts of the present invention are remarkably universal. Use of a single Cr+3 carboxylate results in copolymerization of the various reactants listed above. In contrast, metalloporphyrin catalysts are not universal; that is, different (e.g., Al, Zn) metalloporphyrins are needed to promote the reaction of different polymeric systems. Furthermore, in the case of the metalloporphyrins, usually a protic cocatalyst compound is needed to promote or initiate the reaction. This is not the case with the Cr+3 catalysts of the present invention, in which no additional initiator or cocatalyst is required, although one could optionally be used.
In the chemical reaction systems of the invention, the Cr+3 catalysts significantly increase the reaction rates. The overall reaction times are up to several orders of magnitude faster than existing catalyst systems, thereby significantly improving the process economics by providing considerable savings in labor and equipment productivity factors.
The following detailed description illustrates the invention by way of example, not by way of limitation of the principles of the invention. This description will clearly enable one skilled in the art to make and use the invention, and describes several embodiments, adaptations, variations, alternatives and uses of the invention, including what is presently believed to be the best mode of carrying out the invention.
The reactants are identified throughout by chemical nomenclature with reference to typical commercially available sources, by way of example and not by way of limitation. The reactants are also shown in structural format in the equations. It will be recognized by one skilled in the art that the reaction products may be single molecular species, or more complex mixtures of possible reaction products. Thus, while we have shown in the equations the structural formulas of reaction products, those are by way of example and not by way of limitation of the actual or possible products of the process using the Cr+3 carboxylate catalysts with the reactants shown in the equation. Accordingly, the invention, without limitation, covers novel products of the inventive catalytic process.
A. Description of the Chromium+3 Carboxylate Catalyst
The catalyst of the present invention is a Cr+3 salt. In one embodiment, the Cr+3 salt is a C3-C60, straight or branch-chained, aryl, alkyl or aralkyl carboxylate. For purposes of this application, an xe2x80x9carylxe2x80x9d group is defined as being derived from an aromatic hydrocarbon typically with 6 to 20 carbon atoms, referably 6 to 16 carbon atoms, having a single ring (e.g., phenyl), or two or more condensed rings (e.g., naphthyl), or two or more aromatic rings which are linked by a single bond (e.g. biphenyl). The aryl group may optionally be mono-, di- or tri-substituted, independently, with lower branched or straight chain alkyl, lower cycloalkyl with 3 to 12 carbon atoms, lower branched or straight chain alkoxy, lower cycloalkoxy with 3 to 12 carbon atoms, fluoro, chloro, bromo, trifluoromethyl, cyano, nitro and/or difluoromethoxy, and so forth. The Cr+3 carboxylate of the invention may optionally be a hexanoate, pentanoate, 2-ethylhexanoate, oleate, stearate, toluate, cresylate, benzoate, alkylbenzoate, alkoxybenzoate, napthanate, alkoxide, acetate, butyrate, propionate, octoate, and decanoate. In a preferred embodiment, the Cr+3 salt is a C3-C10, straight or branch-chained, aryl, alkyl or aralkyl carboxylate, such as acetate, butyrate, propionate, benzoate, octoate, and decanoate. In a particularly preferred embodiment of the invention, the catalyst is chromium+3 octoate, where the octoate is a straight or branch-chained C8, that may include either, or both, 2-ethyl-hexanoate or octanoate.
The catalyst can be used as a pure compound or may instead be used with a solvent or diluent, such as an alkyl ester of phthalic acid or a high boiling petroleum distillate. Thus the total chromium content in the catalyst employed will range from about 0.5 to the theoretical maximum for the pure carboxylate compound, e.g. about 10.8% for chromium+3 octoate. In a preferred embodiment, the Cr+3 concentration in the chromium+3 octoate catalyst is from about 4% to about 8%, by weight. The catalyst/solvent system can range in viscosity from very fluid to very viscous.
The chromium+3 octoate catalyst can be prepared in accordance with Example 1 of U.S. Pat. No. 3,968,135, herein incorporated by reference. The preferred chromium+3 octoate concentration in the catalyst is 37.1% to 74.1%, with the balance, 25.9% to 62.9%, being composed of the solvent di-n-heptyl phthalate or a high-boiling petroleum distillate. The solvent in the chromium+3 octoate catalyst is present to aid in the handling of the catalyst, i.e., make it more fluid, dispersible, dispensable and contactible with the reactants in the reaction media and is not an essential component.
The preferred concentration of chromium in the total reaction media is from about 0.08% to about 2.0%, by weight, and more preferably from about 0.1% to about 0.7%, by weight, based on the combined weight of the reactants.
B. Use of Chromium+3 Carboxylate to Promote Aziridine Reactions
1. The Reaction of Aziridines with Carboxylic Acids are Accelerated with Cr+3 Carboxylate Catalysts
(a) Monomeric Systems: Reactions of Monofunctional Aziridines with Monofunctional Carboxylic Acids
One embodiment of the present invention is shown in the following equation: 
where R1 through R5 can be made up of any combination of hydrogen, alkyl, alkene, alkyne, aryl, alkylaryl, cyano, azido, carboxy, oxo, hydroxy, halo or like kind substituted groups and the monofunctional carboxylic acid can be any molecular weight and composition. The result of the reaction will be ring opening with any carboxylic acid to form single addition product esters with diverse functional groups.
One of ordinary skill in the art will recognize that the specific example, Example 1, provided below, demonstrates that chromium+3 carboxylates can catalyze the reaction between an aziridine and any carboxylic acid, regardless of whether the reactants are monofunctional or polyfunctional.
(b) Polymeric Systems: Reactions of Polyfunctional Aziridines with Polyfunctional Carboxylic Acids
Another embodiment of the present invention is shown in the following equation: 
where R1 through R10 can be made up of any combination of hydrogen, alkyl, alkene, alkyne, aryl, alkylaryl, cyano, azido, carboxy, oxo, hydroxy, halo or like kind substituted groups and the polyfunctional carboxylic acid can be any molecular weight and composition provided that it contains at a minimum at least an average of 1.0 equivalents of the carboxylic acid group per mole and the aziridine combination, x and y are each at least 1, denoting a polyfunctional aziridine compound. The result of the reaction will be ring opening to form polyamine-esters containing diverse functional groups.